Various techniques are used on spinning machines in order to resume spinning (yarn production) after an interruption in the spinning process has occurred, whether it is after an accidental yarn break or after a controlled interruption of spinning after receiving a signal from a yarn quality sensor or after the replacement of a fully wound bobbin with an empty tube.
The purpose of the preparation of a workstation for the resumption of the spinning process is to ensure that the individual machine parts of the workstation and, if necessary, also the parts of an attending device, adopt the required position or setting, so that the spinning-in end of yarn is ready to be spun in, and to ensure that the spinning-in end is situated in a defined initial position for starting the spinning-in process.
In the case of a sudden interruption of spinning, e.g., due to a yarn break, it is generally such a fast process that it is not possible to apply the controlled stopping of the workstation of the machine and the torn end of yarn is wound onto the bobbin. So as to resume the spinning process, it is therefore necessary to detect this yarn end on the bobbin by means of an attending device or manually, to remove the faulty yarn portion by unwinding it from the bobbin, and to guide the yarn to its working path or to a position in which it can be easily delivered to the means of the workstation. At the same time, for the resumption of the spinning process, it is necessary for the yarn end to be situated in the so-called transfer position with respect to the spinning nozzle for further operations at the working station and for delivery to the spinning nozzle to perform the final steps of the preparation of the workstation of the air-jet spinning machine for the resumption of the spinning process.
Analogous to this situation is also the preparation of the workstation for the resumption of the spinning process after the replacement of a fully wound bobbin with an empty bobbin, when the yarn end is not detected on the wound bobbin, but it is spun onto auxiliary yarn, which is usually brought by the attending device on a bobbin of auxiliary yarn. The attending device prepares the auxiliary yarn so that it could be promptly delivered to the means of the workstation. The yarn end is placed by the attending device in the so-called transfer position for further operations at the working station and for being inserted into the spinning nozzle so that the final steps of the preparation of the workstation of the air-jet spinning machine for the resumption of the spinning process can be performed.
In the case of a controlled interruption of spinning, e.g., after a signal from the yarn quality sensor, the machine parts of the workstation gradually decelerate in a coordinated manner until they come to a complete stop, i.e. to the interruption of spinning, whereby the yarn remains in the working path at the working station, its end being situated in the spinning nozzle, and so there is no need to detect it on the bobbin or set it to the so-called transfer position for further operations at the workstation and for insertion into the spinning nozzle so as to perform the final steps of the preparation of the workstation of the air-jet spinning machine for the resumption of the spinning process.
The aforementioned final steps of the preparation of the workstation of the air-jet spinning machine for the resumption of the spinning process consist in delivering the yarn end from the transfer position to the spinning nozzle and then in unwinding the required length of the yarn against the direction of the fiber feed to the spinning nozzle in the course of normal spinning in front of the spinning nozzle, where is arranged a device for the preparation of the spinning-in end of yarn, which creates the spinning-in yarn end on the unwound yarn. In the meantime, the other machine parts of the workstation get ready for starting the spinning-in process, including the formation of a yarn reserve in an underpressure yarn storage device by unwinding the yarn from the bobbin. As a result, the workstation is now ready to resume the spinning process. Subsequently, the spinning-in process is started, whereby the individual machine parts of the workstation are started, the yarn begins to be withdrawn by a yarn drawing-off mechanism and wound onto an accelerating bobbin, whereby the difference arising between the drawing-off speed and the rotational speed of the bobbin, which only gradually increases and substantially the immediate acceleration of the yarn by the drawing-off mechanism is compensated for by the underpressure yarn storage device through which the yarn passes during the acceleration of the bobbin to reach the operating speed and which is situated in front of the winding device of yarn. At a pre-defined time point, the start of the yarn withdrawal is followed by the initiation of the feed of sliver to the spinning nozzle and, consequently, the newly formed yarn is connected to the spinning-in end of yarn in the spinning nozzle.
The above-mentioned techniques are disclosed, for example, in the solution according to DE 10 2012 108 380 A1.
The problem of the background art is the continuing certain variability of the position of the spinning-in yarn end, which is created by interrupting the yarn, usually by tearing the yarn in a device for the preparation of the spinning-in yarn end, which consequently negatively affects the uniformity of the piecers at one workstation, as well as at different workstations. Another drawback is the fact that part of the yarn with the spinning-in yarn end, i.e. the part which passes through the spinning nozzle and during spinning-in the newly formed yarn is connected to its end, i.e. to the spinning-in end, has only a limited length defined by the length of the yarn path between the device for forming the spinning-in yarn end and the spinning nozzle. In some cases this length appears to be insufficient, since for high-quality and uniform piecers it is advantageous if the spinning-in yarn end reaches a certain speed at the moment of the connection and moves at a relatively constant speed.
The aim of the invention is therefore to eliminate or at least minimize the disadvantages of the background art.